Numerous devices have been suggested in the prior art to avoid collision between occupants in a vehicle and elements of the vehicle as a result of an external collision. These devices include a variety of restraining systems intended to keep the occupant(s) in a relatively fixed position in relation to the interior of a vehicle. Inflatable bags have been described wherein the uninflated bag is strategically positioned such that, when inflated, the bag presents a resilient cushion to receive and absorb the energy of an occupant being displaced as a result of a vehicular collision.
Inflatable bag systems are associated with numerous technical difficulties, including but not limited to, the complexity of the inflating media, the limitation on the quantity of survival units that may be safely installed in a single closed vehicle and the predictable timely collapse of the unit to aid in the occupant's egress from the damaged vehicle. In order for an occupant restraint system to be effective, it must assume a certain minimum volume within a few milliseconds of receipt of a trigger signal to function. This presupposes the storage of an inflating media in sufficient quantity to accomplish the required inflation function. The larger the restraint cushion (bag) the more of the inflation media that is required. Current technology usually provides either a chemical gas producing media, usually activated by controlled combustion or a stored high pressure gas source that inflates the bag upon its release, or, a combination of both, usually referred to as a "hybrid" system. The system described herein addresses these problems through a design that uses ambient air to inflate approximately 90% of the inflatable volume and a chemical gas producer, or, high pressure stored gas to inflate the remaining 10% of the bag free volume. In addition, the prepackaged system must be of such a design to minimize its size and weight as well as its simplicity of function when it is provided the correct trigger signal.
A factor which greatly affects the ability of an inflatable system to cope with the "minimum" design criteria is the rising atmospheric pressure within the vehicle as the inflatable bag expands. The total volume of one or more fully expanded bags represents a sizable proportion of the total vehicular closed volume; in view of the necessity for rapidly expanding the bag, the atmospheric pressure within the vehicle increases as the bag rapidly expands. This increasing atmospheric pressure further complicates the performance of most conventional systems by requiring the stored gas system to provide even greater pressure to fill the bag as the bag expands and pushes against the increasing ambient air pressure.
The general design and performance parameters of typical air bag function requires that the air bag accomplish extremely rapid inflation and then an equally rapid deflation so that a total cycle is anywhere from 50 to 100 milliseconds in length. This requirement usually is vague regarding the time cycle requirement versus the actual impact "G" force experienced by the occupant. As an example, in an 5G impact, the air bag can inflate and proceed to the deflated status in the 50 to 100 millisecond time frame, however, the same 5G impact can become 10 or 15 or even 20 g's if the impact cause is moving at any higher velocity than that required to generate the 5G level. At the higher g level the air bag will deflate in a shorter time frame, allowing the kinetic energy of the occupant to deteriorate much less than in the 5G impact and, thus, create a circumstance where the elevated level of residual kinetic energy is likely to be absorbed as the occupant travel deflates the air bag and then proceeds to impact the air bag surrounding structure.